Newer diesel engines have diesel particulate filters (DPFs) incorporated in their exhaust systems to filter carbon and other particulates from the exhaust gas stream. When enough particulate material has accumulated on or around the filter element, the DPF begins to plug and requires regeneration. Regeneration is a process whereby deposits on the filter element of the DPF are induced to combust, typically by raising the engine exhaust temperature. The combustion event of a DPF regeneration cleans the filter element of the DPF of deposits by burning carbon accumulations and turning them into ash. The regeneration process repeats as often as necessary to maintain smooth and reliable engine operation.
In many diesel engines, an electronic control unit (ECU) controls and monitors the operation of engine components. The ECU typically sends commands to various systems of the engine, including commands intended to trigger regeneration of a DPF. One parameter of great importance to regeneration of the DPF is the pressure difference upstream and downstream of the filter element of the DPF. The pressure difference across the DPF can be correlated to the extent of the filter's plugging with carbon and other deposits. By obtaining a reliable and accurate measurement of the pressure differential across the DPF, the engine controller may initiate a regeneration event at an optimal time.
Typical engines have at least two pressure probes or sensors installed across a DPF filter, or other components in the exhaust system. Typical pressure probes include a tube that is inserted perpendicularly to an exhaust pipe segment, usually in a radial direction with respect to a centerline of the pipe segment. A typical installation of pressure probes in an exhaust system can been seen, for example, in U.S. Pat. No. 6,851,258 by Kawashima et al. Typical installations of pressure sensor probes are prone to fouling of the probes, yielding inaccurate readings of the pressure sensors attached to them.
Many different attempts to rectify the fouling of sensors have occurred in exhaust systems. Permeable shields, as can be seen for example in U.S. Pat. No. 6,551,498 by Nelson, have been used to protect sensors from the ill effects of carbon or other deposits on the sensing passages and elements. These solutions are costly and may create new problems. When using pressure sensor probes, one may desire little to no obstruction of the sensor probe, so as to not impede gas dynamics in the probe that are required for accurate sensor readings. Use of a shield with a pressure probe will likely impede optimal sensor operation.
Accordingly, there is a need for a method of protecting pressure sensor probes placed in an exhaust system of an engine that is cost effective and does not affect the operation of the sensor.